1. Field of the Invention
This invention relates generally to a system for making open-ended belting reinforced with a tensile cord layer that is totally encapsulated, without use of mold flights or noses.
2. Description of the Prior Art
Conventional processes of continuous extrusion-forming of thermoplastic elastomer (“TPE”) or thermoplastic urethane (“TPU”) reinforced belt profiles utilize a rotatable molding wheel which is supplied with a molding band (usually of flexible steel) wrapping around about half of the circumference of the molding wheel to form a rotating molding chamber into which cords are fed along with extruded belt material. For making toothed belts, the molding wheel has teeth with winding noses or flights on the mold teeth to support the reinforcing cord and thus set the pitch line differential (“PLD”) of the belt. The use of noses or flights results in cord exposure to the environment in the land area between each tooth of the finished belt. The lack of cord support on a pulley in the exposed nose region also contributes to failure of the tensile member (especially for aramid cords) when the belt is subjected to dynamic flexing. An example of a conventional process using winding noses is disclosed in U.S. Pat. No. 3,880,558 to Breher et al.
For steel wire tensile members, the cord exposure necessitates special (expensive) corrosion-resistant steels or coatings, such as a zinc coating applied to each individual filament. Post processing steps can be added to fill in the nose regions with additional thermoplastic material to protect the cords, but at additional effort and expense.
Another method of eliminating the nose region includes a specially designed dual-nozzle extruder die which places a layer of thermoplastic on the mold teeth before the cord arrives thereon, as also disclosed in U.S. Pat. No. 3,880,558 to Breher et al. However, this method does not make it easy to control the belt PLD.
Another method of eliminating the nose region includes inserting a tooth covering fabric onto the mold before the cord is placed thereon as disclosed in U.S. Pat. No. 4,515,743 to Breher. This method adds fabric expense and changes the nature of the belt surface, which may not necessarily be desirable.
Another method suited for making flat belts is disclosed in U.S. Pat. No. 6,966,763 to Goser et al., in which two layers of material are applied by two separate extrusion stations.
Mention is made of the applicants' co-pending U.S. application Ser. No. 13/715,989 filed on Dec. 14, 2012, titled “Apparatus and Method for Making Endless Reinforced Belts,” claiming the benefit of provisional application 61/570,814 filed on Dec. 14, 2011, the entire contents of which are hereby incorporated herein by reference.
Conventional extrusion systems using some type of cross head die with tensile cords passing through have practical limitations with respect to producing wide belt sections. Belts wider than about two feet are not practical.
What is needed is an improved method of making continuous, open-ended, reinforced thermoplastic, profile belting, capable of much wider belt widths.